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Type Coercion

L4 provides built-in type coercion functions that are always available without importing any library. These are implemented in the compiler core for performance and consistency.

Functions

TOSTRING

Converts a value to its string representation.

Signature: NUMBER | BOOLEAN | DATE | STRING → STRING

Behavior:

  • Numbers render with canonical decimal text (no trailing zeros)
  • Booleans render as TRUE or FALSE
  • Dates render as YYYY-MM-DD
  • Strings pass through unchanged

Example:

-- Type Coercion Example: Built-in conversion functions
IMPORT daydate

-- TOSTRING: Convert values to strings
DECIDE numberText IS TOSTRING 1.20
#EVAL numberText  -- "1.2" (no trailing zeros)

DECIDE boolText IS TOSTRING TRUE
#EVAL boolText  -- "TRUE"

DECIDE dateText IS TOSTRING (Date 29 2 2024)
#EVAL dateText  -- "2024-02-29"

-- AS STRING: Inline syntax (same as TOSTRING)
DECIDE boolAsString IS TRUE AS STRING
#EVAL boolAsString  -- "TRUE"

DECIDE dateAsString IS (Date 1 1 2024) AS STRING
#EVAL dateAsString  -- "2024-01-01"

-- TONUMBER: Parse strings to numbers
DECIDE parsedGood IS TONUMBER "  -12.50 "
#EVAL parsedGood  -- JUST -12.5

DECIDE parsedSci IS TONUMBER "1.2E3"
#EVAL parsedSci  -- JUST 1200

DECIDE parsedBad IS TONUMBER "oops"
#EVAL parsedBad  -- NOTHING

-- TODATE: Parse strings to dates
DECIDE parsedISODate IS TODATE "2024-02-29"
#EVAL parsedISODate  -- JUST (Date 29 2 2024)

DECIDE parsedSlashDate IS TODATE "15/01/2024"
#EVAL parsedSlashDate  -- JUST (Date 15 1 2024)

DECIDE parsedNamedDate IS TODATE "Feb 01, 2024"
#EVAL parsedNamedDate  -- JUST (Date 1 2 2024)

DECIDE parsedBadDate IS TODATE "31/02/2024"
#EVAL parsedBadDate  -- NOTHING (Feb 31 doesn't exist)

-- TRUNC: Truncate decimal places
DECIDE truncWhole IS TRUNC 12.987 0
#EVAL truncWhole  -- 12

DECIDE truncDecimals IS TRUNC 12.987 2
#EVAL truncDecimals  -- 12.98

DECIDE truncNegativeDigits IS TRUNC 123.45 (0 MINUS 1)
#EVAL truncNegativeDigits  -- 120

DECIDE truncNegativeNumber IS TRUNC (0 MINUS 123.45) 1
#EVAL truncNegativeNumber  -- -123.4

-- Combining coercions with pattern matching
GIVEN input IS A STRING
GIVETH A STRING
parseAndDouble input MEANS
    CONSIDER TONUMBER input
    WHEN NOTHING THEN "Invalid number"
    WHEN JUST n THEN TOSTRING (n TIMES 2)

#EVAL parseAndDouble "21"    -- "42"
#EVAL parseAndDouble "abc"   -- "Invalid number"

TONUMBER

Parses a string to a number.

Signature: STRING → MAYBE NUMBER

Behavior:

  • Accepts trimmed ASCII numeric literals
  • Supports optional sign (+ or -)
  • Supports decimal point
  • Supports scientific notation (e.g., 1.2E3)
  • Returns NOTHING on parse failure

Accepted formats:

  • "42" → JUST 42
  • "-12.50" → JUST -12.5
  • " 3.14 " → JUST 3.14 (whitespace trimmed)
  • "1.2E3" → JUST 1200
  • "oops" → NOTHING

TODATE

Parses a string to a date.

Signature: STRING → MAYBE DATE

Accepted formats:

  • YYYY-MM-DD (ISO 8601): "2024-02-29"
  • YYYY/MM/DD: "2024/02/29"
  • DD-MMM-YYYY: "29-Feb-2024"
  • DD/MM/YYYY: "29/02/2024"
  • MMM DD, YYYY: "Feb 29, 2024"

Behavior:

  • Month names are case-insensitive
  • Rejects dates outside 0001-01-01 to 9999-12-31
  • Returns NOTHING for invalid dates (e.g., "31/02/2024")

TRUNC

Truncates a number toward zero.

Signature: NUMBER, NUMBER → NUMBER

Parameters:

  • value - The number to truncate
  • digits - Number of decimal places to keep (rounded to nearest integer)

Behavior:

  • Non-negative digits truncate fractional places
  • Negative digits truncate to the left of the decimal point
  • Truncates toward zero (not floor/ceiling)

Examples:

  • TRUNC 12.987 0 → 12
  • TRUNC 12.987 2 → 12.98
  • TRUNC 123.45 (-1) → 120
  • TRUNC (-12.987) 1 → -12.9

AS STRING

Inline syntax for type conversion, equivalent to TOSTRING.

Syntax: value AS STRING

Examples:

  • 42 AS STRING → "42"
  • TRUE AS STRING → "TRUE"
  • (Date 1 1 2024) AS STRING → "2024-01-01"

Locale Independence

All coercion functions are deterministic and locale-independent. This ensures consistent behavior across different systems and environments.

See Also